This invention relates to a knock sensor for detecting knocking of an engine for automotive vehicles.
Knocking of an automotive vehicle is considered to be a factor which is detrimental to the smooth running of the vehicle, the durability of the engine and the improvement of fuel consumption. As regards the measures taken to counter knock, it is known in the art that the knock can be readily eliminated by controlling the ignition timing, the air-fuel mixture ratio or the like. The known knock sensors are generally so designed that the knock condition is detected from the peak of a spectrum generated as a vibration waveform of the engine of a vehicle and the frequency of the peak which varies in dependence on the type and size of engines is in the range of 6 to 9 kHz. Since variation in the spectrum is picked up in the vicinity of the vehicle engine where the S/N ratio is extremely inferior electrically, the sensitivity-frequency characteristics of the knock sensor for vibrations should preferably be such that the resonant frequency corresponding to the frequency of the peak has a high quality factor as shown in FIG. 1.
Also the knock sensor should preferably be so constructed that it can be mounted to an engine easily.